Control system for vapor generators



March 12, 1957 E. D. scuTT CONTROL SYSTEM FOR VAPOR GENERATORS FiledNov. 23, 1953 5 Sheets-Sheet l March 12, 1957 E. D. SCUTT CONTROL SYSTEMFOR VAPOR GENERATORS 5 Sheets-Sheet 2 Filed NOV. 23, 1953 March 12, 1957E. D. scuTT CONTROL SYSTEM FOR VAPOR GENERATORS 5 Sheets-Sheet 3 FiledNov. 23, 1953 E. D. SCUTT CONTROL SYSTEM FOR VAPOR GENERATORS March 12,1957 5 Sheets-Sheet 4 Filed NOV. 23, 1953 March 12, 1957 E. D. scuTTCONTROL SYSTEM FOR VAPOR GENERATORS 5 Sheets-Sheet 5 Filed Nov. 25, 1955United States Patent 2,784,912 CONTROL SYSTEM non vAPon GENERATORS EdwinD. Scott, Willow Grove, Pa., assignor to Leeds and Northrup Company,Philadelphia, Fa, a corporation of Pennsylvania Application November 23,1953, Serial No. 393,815 Claims. (Cl. 236- 44 This invention relates tocontrol systemsjfonvapor generators of the type delivering vapor to acommon line and including two independent furnacesandhas for an objectthe provision of means for varying the fuel supplied to each furnace tomaintain optimum conditions of combustion of fuel with any selectedratio of heat generation within the respective furnaces.

Though the present invention is applicable to vapor generating units ofwidely differing design, it has particular usefulness in applicationswhere the vapor or steam requirements are quite high. For example, somepresent-day turbine generators have capacities of 200,000 kilowatts andabove. As the boiler capacities have been increased to meet such heavyloads, furnaces for them have been subdivided into severalfcombustionchambers as a means of overcoming constructional, combustion, and heattransfer problems encountered in connection with the larger units.

In one type of boiler, known as a split-furnace boiler, the paths forcombustion. gases come together beyond the two combustion chambers.Another type,known as a twin-furnace boiler, has, in effect, twoseparate furnaces in that fuel supplies thereto and passages forcombustion gases therefrom are entirely separate. This type isparticularly advantageous when steam returned from ahigh pressureturbine is tohe reheated and again ,fed to a turbine. With completelyseparate gas passages for the two furnaces, and with location of thereheater section in one furnace only, that furnace may be independentlybrought up to temperature, but only after steam is availableto passthrough the reheater, thus avoiding overheating of the reheater section.

Twin-furnace boilers present unusual control problems, since while thefurnaces are separate, there is only one steam pressure and one steamflow which can be measured for purposes of control. New methods aretherefore required toassure that each furnace is operated with highefficiency while supplying its proper share of the heat.

The present invention is particularly useful when furnaces of theforegoing type utilize coal as fuel. .As is well understood by thoseskilled in the art, pulverizers are in general located adjacent thefurnace with delivery of pulverized coal directly to the tire chamber.While there is a more orless regulated flow of coal to the fire chamber,as by adjustment of the speeds of the coal feeders which deliver thefuel to the pulverizers, nevertheless, a number of factors contribute tosubstantial irregularity in the amount of coal delivered per unit oftime at a given speed of operation. Whenthere is superimposed on such.variables a varying B. t. u. contentof the coal, the heat content of thefuel delivered in unit-time may represent a variable of substantialmagnitude and may give rise to unequal heating conditions inthe severalfurnaces and to undesirable conditions of combustion andheatdistribution.

In carrying out the present invention in one form thereof, advantage istaken of the fact that combustion 2,784,912 Patented Mar. 12, 1957efiiciency is related to the oxygen content of the products ofcombustion from each furnace. Accordingly, with the oxygen content at apredetermined value, .it will be known that the conditions of combustionfor the fuel are maintained at optimum values. There is provided asensitive means exposed to the combustion products from each furnace fordeveloping an outputwhich varies with the efficiency of combustion offuel within each furnace.

.While oxygen may be preferred as a component. of products of combustionselected to vary the output of such an element, it is to be understoodthat another component or a product of the combustion may be utilized toproduce a variable output which is indicative of efficiency of fuelcombustion within the furnace. While variation in such output can beutilized to vary the relationship between fuel delivery and combustionair, it is preferred to predetermine the flow of combustion airinaccordance with the steam flow in the delivery line to adjust thetotal fuel to the two furnaces to maintain the steam, pressure, andrelatively to adjust the rate of fuel delivery to each furnace toequalize the combustion conditions between the furnaces throughmaintaining the difference between the outputs of said sensitiveelements at a predetermined value, generally zero.

For further objects and advantages of the invention and for a moredetailed description thereof, reference is to be had to the followingdescription taken in conjunction with the accompanyingidrawings, inwhich:

Fig. l illustrates, partly by block diagram and partly diagrammatically,one embodiment of the invention;

Fig. .2. diagrammatically illustrates a control system for regulatingthe supply of combustion air to the furnaces;

Fig. 3 diagrammatically illustrates the control system for maintainingpredetermined pressure conditions within thefurnaces;

Fig. 4 diagrammatically illustrates a preferred form of an oxygendetecting system for the several furnaces; and

Fig. 5 diagrammatically illustrates a modified form of the. invention.

Referring to. Fig. l the invention has been shown in one form as appliedto a vapor generator or steam boiler 10 of the multiple furnace type.One furnace 11 has its own steam heating sections schematicallyrepresented by the coils 12a and 1211, its own means for regulating theflow of combustion air therethrough, as by the dampers 13,.and its ownfuel burners 14a and 1412. A second furnace 15 has its own steam heatingsections represented schematically by the coils 16a and 16b, its ownmeans for regulating the flow of combustion air therethrough comprisingthe dampers 17 and its own burners 18a and 18b. The burners 14a and 14])are' supplied with powdered coal from pulverizers 20, while the burners18a and 18b are supplied from pulverizers 21.

Mention has already been made of the fact that the steam coils 12 and 16are but diagrammatic representations of conventional arrangements ofsteam heating sections which may, and will, be provided in each offurnaces 1 1 and 15. For example, in furnace 11 there may be included asteam generating section, a primary superheatersection 12a and asecondary superheater section 12b, while the other. furnace 15 maybeprovided with a steam generating section, a primary superheater section16a and a reheater section 16b, these being supported in conventionallocations within each furnace. As shown in Fig. 1, however, the gasesand products of combustion flow from each furnace through ducts 22 and23 leading to a stack 24. In the passageway to the stack there isincluded a fan 25 for applying an induced draft to both of the ducts 22and 23 and thence to the furnaces 11 and 15. i

end of the arm 60a.

A source of vapor for coils 12 and 16 is represented by a steam drum 27,the superheated steam from coils 12a, 12b and 16a being delivered by wayof a common line 28 to a steam header 29 for the supply of steam to theturbine-generator units, only one of which, the unit 30, being shown.

In order to equalize and to maintain at optimum conditions thecombustion of fuel, powdered coal, for each furnace, there is providedin each of them a sensing device'for producing an output which varieswith efficiency of the combustion of the fuel. More specifically, forfurnace 11 such a device 31 having a gassampling line 31a produces anoutput varying with the amount of oxygen present as a component of theproducts of combustion. Similarly, for furnace 15a device 32 having agas-sampling line 32a produces an output which varies with oxygen as acomponent of the products 'of combustion.

The manner in which each of the devices 31 and 32 functions will belater explained in connection with more detailed showings of onesuitable type of equipment, it being sufficient for the purposes of Fig.1 to say that the device 32 serves relatively to adjust the position ofa slidewire contact 33a relative to its slidewire 33, similar relativeadjustment occurring as between slidewire 34 and its associated contact34a as a result of operation of device 31.

Slidewires 33 and 34 are connected in an electrical bridge or network 35developing an output applied to a control system represented by a block36 for applying control signals to conductors 37 and 38 depending uponwhether the oxygen content in furnace 11 is greater or less than theoxygen content in furnace 15 as indicated by devices 31 and 32.

If the oxygen content in furnace 11 exceeds that in furnace 15, currentflows under the control of system 36 as from a supply line 39 by way ofconductor 38 to a motor 40 and to the other supply line 39a. The motor40 is thereupon energized for rotation in a direction which throughassociated apparatus increases the speed of coal feeders 20a anddecreases the speed of coal feeders 21a.

If the oxygen content in furnace 15, as detected by device 32, risesabove that in furnace 11, it will be understood that the control system36 will apply through conductor 37 a control signal for reverseoperation of motor 40 again to equalize the oxygen content in the twofurnaces by relatively changing the rate of fuel delivery to them.

The speeds of operation of coal feeders 20a and 21a are adjusted by theoperation of motor 40 by any suitable means, the one illustratedincluding speed adjusters similar to the type known as Reeves drives.More particularly, a pair of motors 41 drives coal feeders 20a through apair of Reeves drives 42, while a pair of motors 43 drives coal feeders21a through Reeves drives 44. Motors 46 respectively serve to adjust theReeves drives 42, the motors being connected in parallel to controlconductors 47 and 48. Similarly, motors 49 connected in parallel tocontrol conductors 50 and 51 serve to adjust the Reeves drives 44.

The coal feeder speed-adjusting motors 46 are energized under thecontrol of a Kelvin balance 60 having coils 61-64, the energization ofwhich positions a control arm 60a to complete a circuit from a supplyline 65 through a movable contact and one or the other of stationarycontacts to one or the other of control conductors 47 and 48. Theposition of the control arm 60a of the Kelvin balance 60 likewisedepends upon the pressure applied to it by a diaphragm of apressure-responsive'device 66 as through an element bearing against anAs will later be explained in detail, the force applied to arm 60a bydevice 66 varies in response to changes of pressure within steam header,29. If the steam pressure in header 29 decreases, the

arm 60a is moved to close a circuit through conductor 47 to energizemotors 46 in directions to increase the speed of operation of coalfeeders 20a. The circuit ex-' tends from supply line 65 by way of themovable contact, the left-hand stationary contact, conductor 47 andthrough the respective motors 46 and thence to the other supply line 67.As shown, the coils 61 and 62 produce opposing magnetic fluxes, whilethe coils 63 and 64 produce fluxes which develop attractive forces.Thus, the respective pairs of coils 61-62 and 6364 tend to rotate arm60a in a clockwise direction about pivot 68, the movement being opposedby the thrust developed by pressure-responsive device 66.

By including in the energizing circuit of coils 61-64 an autotransformer70, several purposes are served. First, upon energization of motors 46,and through mechanical connections 46a and 46b, autotransformers 71 and72 are adjusted to produce an increased output voltage with increasingspeed of operation of the coal feeders; and a decreasing output for adecreasing speed of operation of the coal feeders.

The outputs from transformers 71 and 72 are applied to the primarywindings of insulating transformers 73 and 74. They have their secondarywindings connected in series-aiding relationship in a series-circuitformed by conductors 76 and 77 leading to the autotransformer 70.

An increase in pressure on device 66 causes arm 60a to move in acounterclockwise direction. The resultant operation of autotransformers71 and 72 increases the energization of autotransformer 70. Theincreased energization of the coils of the Kelvin balance increases theclockwise torque applied to arm 60a to bring about a new balance withthe movable contact in open-circuit position and with the coal feedersoperating at the newly established increased speed.

The second function performed by the autotransformer 70 and itscounterpart 70a, associated with a Kelvin balance 80, is produced by theoperation of the motor 40 in one direction or the other under thecontrol of the oxygen-responsive system including network 35. As alreadyexplained, when the oxygen content in furnace 11 differs from that infurnace 15, the motor 40 is energized in a direction which changes theoutput of autotransformers 70 and 70a for operation of the respectiveKelvin balances 60 and 80 to vary the speeds of operation of the coalfeeders until the oxygen contents in furnaces 11 and 15 are equalized.It is to be understood, of course, that motor 40 moves adjustablecontact of autotransformer 70 to increase its output at the same time itmoves the adjustable contact of transformer 70a to decrease its output,and vice versa.

The pressure-responsive devices 66 and 81 associated with the respectiveKelvin balances 60 and 80 directly affect the position of the controlarms 60a and 80a. Thus the primary response of the control system is tosteam pressure in header 29. The adjustment of arms 60a and 80a withchange of setting of autotransformers 70 and 70a represents a secondaryadjustment. The described operation under the control of theoxygen-responsive bridge 35 has been termed a secondary eifect for thereason that in normal operation only a small adjustment ofautotransformers 70 and 70:: will be required to equalize the oxygencontents in the respective furnaces 11 and 15 to maintain optimumconditions of combustion.

Though more extensive changes in the speeds of operation of the coalfeeders may be obtained in accordance with the invention, otherprovisions for the control of combustion conditions result ordinarily inthe need for only limited adjustment of autotransformers 70 and 70a.

There will now be explained some of the other provisions for procuringoptimum conditions of combustion offuel. To large extent, the combustionair supplied to each furnace is determined in accordance with steam fl wthrough the common steam line 28 extending to heade 2 s. he am un o ombuist ir or th ,ratejat which it flows is related to the load to becarried in Fig. 2, will be later described.

In the vapor or steam generator 10 of Fig. 1, a number of desirableconditions of operation are met in addition to those which havejust beenoutlined. As is well understood, the fan applies an induced draft tofurnaces 11 and 15. The magnitude of the induced draft is under thecontrol of dampers 8 4 adjustable as by a control device 85. Device 85adjusts dampers 84 to predetermine the ratio of total air flow to bothfurnaces with respect to the steam flow in the common line 28.

Dampers 13 and 17 respectively in furnaces 11 and 15 are adjusted tomaintain equality or predetermined bias or difference in flow ofcombustion air as between the two furnaces.

A fan 83 is provided for applyingforced draft to the furnaces 11 and 15.The magnitude of that draft is regulated by dampers 88, adjusted bydevice 89 to maintain a desired average pressure within the two furnacesas compared to the external pressure. In; general, aslight negativepressure within the furnace relative to ambient pressure represents adesirable condition.

When one or the other of dampers 13 and 17 is moved toward a closedposition to decrease the flow of combustion air, there will be acorresponding adjustment of be moved toward closed position forequalization of furnace pressure, dampers 13 and 86 under the assumedconditions remaining in their open positions.

There will now be described the manner in which the pressures applied bydevices 66 and 81 to the Kelvin balances and are varied in response tosteam pressure in header 29. The pressure in header 29 is applied by apipe 91 to a pressure-responsive element, as a Bourdon tube 92, forminga part of a master controller93.

The master controller 93 may be constructed in the manner fullydescribed in McLeod Patent No. 2,507,606 to which reference may be madefor a more detailed description, or it may be similar to the schematicillustration thereof as appearing in Fig. 1.

An increase in pressure in header 29 causes the Bourdon tube 92, througha push rod 94, to move a control lever in a clockwise direction about aspring-pivot 96. A

decrease in pressure causes Bourdon tube 92 to move to the left, as byspring 97, the push rod 94 and the control lever 95 also moving to theleft by reason of the spring bias produced by the spring-hinge 96. Themovement of a baffle 98 toward and ,away from a nozzle 99 varies thepressurein an output line 100 under the control of a pneumatic relay 101supplied with air pressure from a suitable source of supply as indicatedby the air supply line 102.

With an increase in steam pressure on Bourdon tube 92 baffle 98 is movedaway from nozzle 99, thus reducing the pressure on the pneumatic relayor booster 101 and likewise reducing the air output pressure in line100. The effect upon the Kelvin balances 60 and 80 has already beendescribed, the reduction in pressure in line 100 resulting in clockwiserotation of control arms 60a and 3011 with resultant completion of motor.circuits to the right-hand stationary contacts to reduce the rate ofsupply of fuel to the respective furnaces 11 and 15. Though notessential, there has been shown proportional bellows 105 and resetbellows 106 associated with an auxiliary control arm 107, spring-pivotedat 108 and having its opposite end spring-centered as by a pair ofsprings 109. The proportional bellows 105 is connected to output line110 through a rate adjustment valve111 which introduces a rate action inthe operation of the device. The reset bellows 106 is connectedto outputline 110 by way of a reset adjustment valve 112 and introduces resetaction into the operation.

The booster or pneumatic relay represented by the block 101 correspondswith the booster 560i said McLeod patent, and in that patent there willalso be founda description of how the proportional b and may be'adjustedas desired, the manner in which the reset bellows 106 corrects for droopand the manner in which the rate valve 111 provides the rate actionalready mentioned.

With the fuel delivery determined by the master controller 93, it willnow be seen that if the fuel delivery to the furnace 11 differs fromthat to the furnace 15, there will be excess air or excess fuelin theone as againsfthe other. 1 Accordingly, the oxygen content of theproducts of combustion will differ, and in response to sensing devices31 and 32 an output signal will be applied to pile of conductors 37 and38 for energization of motor 40 in a direction to increase theenergization of the coils of oneKelvin balance and to decrease theenergization of the coils in the other Kelvin balance. Thus, there isprovided the further control action varying the operation of the coalfeeders. The rates of fuel delivery to the two furnaoes are changedeonebeing increased and the other decreased, untilthe oxygen content of theproducts of combustionare equalized or brought to values maintaining apredetermined difference between them. That predetermined diiference maybe readily adjusted by. operation of a knob 115 for relatively adjustingslidewires 116 and 117 in the bridge 35 for balance of the bridge withrelativelydifiering outputs from the devices 31 and 32.

Referring now to Fig. 2, there will be described the system whichautomatically establishes a predetermined flow of combustion air to thetwo furnaces 11 and 15 in response to the rate of flow of steam from thetwo furnaces, as for example, through the header 29. The systemautomatically varies the combustion air with change of flow of steam andin direction to increase the combustion air and, hence, to increase thecombustion rate with increased steam flow and to decrease the combustionrate on decreased steam flow. As greater loads are imposed upon theturbine-generator, it will beunderstood by those skilled in the art thatthe amount of steam flowing from header 29 to the turbine will beincreased, and as the load on the turbine-generator is reduced, thesteam flow to the turbine will be decreased.

As shown in Fig. 2, an indication or measurement of steam flow in header29 is obtained by means of the pressure differential across arestriction shown as a venturi 29a. A high-pressure line 120 applies thehigh pressure to the left-hand side of a tilting manometer 121, and alow-pressure line 122 from venturi 29a is connected to the right-handside of the manometer 121. With varying differential pressure, themanometer 121 will rotate or tilt to the right or to the left about afulcrum 123 to move a contact 12410 the right or to the left forenergization from supply lines 125 and 126 of the device or motor 85 forrotation in a direction to adjust dampers 84 to vary the total flow ofcombustion air through the furnaces 11 and 15 in accordance with changesin steam flow.

As shown in Fig. 2 the level of liquid in the tilting manometer 121 ismuch higher on the right-hand leg and, hence, the resultantdiiferential-pressure torque tends to rotate the manometer in aclockwise direction. This torque is opposed by a torque applied througha link 127, connected at its upper end to a nut or threaded carriage ona threaded rod 123, and at its lower end connected to a diaphragm 129.As later explained, a pilot air flow in line 134 containing restriction133 is maintained proportional to total combustion air flow. Thedifferential pressure across restriction 133 is applied to diaphragm 7129 in the direction to produce a downward pull on link 1 27 and therebyexert a counterclockwise torque on manometer 121. The two torques areautomatically balanced through the operation of motor in adjustingdampers 84, as earlier described.

If it be desired to change the ratio of flow as between steam flow inheader 29 and air flow in line 134, it is only necessary to move theconnection of link 127 toward or away from the fulcrum 123 of thetilting manometer. As shownflthis is accomplished by energization of amotor to rotate the threaded rod 128 to move the end of link 127 to theright or to the left. Though the motor may be controlled automatically,a single-pole, doublethrow switch 13511 is shown as operated to theright or to the left to energize the motor for forward or reverseoperation.

The flow of pilot air from a supply regulator 130 by way of pipe 134 ismade proportional to the total flow of air through the furnaces 11 and15 in the manner now to be described.

The flow of air through the furnace 11 is determined from the drop ofpressure across a flow restriction within the furnace. This restriction,which is represented by a baffle 11a, will ordinarily be the restrictionintroduced by a bank of tubes or other furnace structure. Lines 137 and138 respectively extending from the high and low pressure sides ofbaflle 11a are connected to a tilting manometer 139 which, as a resultthereof, has applied to it a torque tending to rotate it in a clockwisedirection. That torque is opposed by the air pressure applied to theupper side of a diaphragm 140, being the air pressure in a line 141.Line 141 is terminated by a flow restriction 142, flow of airtherethrough being under the control of a pressure regulator 143interposed between line 134 and line 141. The regulator 143 includes avalve element connected to a diaphragm 143a exposed on its upper side tothe pressure in line 141 and on its lower side to the pressure appliedby way of a line 144. Thus, the valve is moved between open and closedpositions in accordance with the differential of pressure acrossdiaphragm 143a. As shown, the valve element is biased toward openposition by a spring, though it may be omitted if desired.

The pressure in line 144 is determined by the position of a valve 145 ofthe throttling or leak-port type. from a suitable source is applied atconstant pressure by way of regulator 146 to the valve 145 whichproduces in line 144 and against diaphragm 143a a pressure varying withthe position of the valve stem 145a. That valve stem is positioned bythe control element 13% of tilting manometer 139. Thus, as the flow ofair through furnace 11 increases, the differential pressure applied tomanometer .139 increases and the manometer rotates in a clockwisedirection to reduce leakage at valve 145 and to increase the pressureagainst the lower side of the diaphragm 143a. This moves the valveelement of the regular 143 toward open position and increases the pressure in line 141. The resultant increase of pressure applied todiaphragm 141i restores balance of the manometer 139 in its newposition. The flow of air through the restriction or orifice 142 is thenproportional to the flow of air through the furnace 11. It follows thenthat the pressure above atmosphere within line 141 is proportional tothe differential of pressure across bafllc 110.

A tilting manometer 149 is connected by lines 151i and 151 across abaffle 15a of furnace 15. By means of a pressure regulator 152, a valve153 and a diaphragm 154 there is maintained in line 155, a pressureabove atmospheric, proportional to the ditferential of pressure acrossbaffle 15a and a flow of air through orifice 1.56 porportional to theflow of combustion air through furnace 15.

Inasmuch as the air flow through restriction 142 is proportional to theflow of combustion air through furnace 11 and the flow of air throughrestriction 156 is proportional to combustion air through furnace 15, itfollows til arsenic.

at once that'the flow of air through line 134 is proportional to thesum, i. e., to the total flow of combustion air to the two furnaces 11and 15. It is in this manner that the manometer 121 responds todeviations from a predetermined ratio between steam-flow in header ,29and flow of total combustion air to the two furnaces.

In order to maintain a predetermined division of combustion air asbetween furnaces 11 and 15, provision is made relatively to adjustdampers 13 and 17. As shown, a motor 160 operates an actuating member161 to move dampers 17 toward closed'position with dampers 13in fullyopened position or to move dampers 13 toward closed. position withdampers 17 in fully open position. This is accomplished by rotation ofmember 161 against one or the other of push rods 162 and 163respectively connected to move dampers 13 and 17 between open and closedpositions, each push rod being provided with a spring normally biasingthe associated dampers in the open position. The motor 160 is rotated inone direction or the other under the control of a tilting manometer 164,one side of which is connected by a line 165 to the line 155, and thusthe pressure applied to the manometer through line 165 is proportionalto the differential of pressure across bafile 15a and, hence, isrepresentative of the flow of combustion air through furnace 15. If theother connecting line 166 of manometer 164 be directly connected toline- 141, the manometer 164 will respond to any differences betweenpressure differentials across baffie 15a in furnace 15 and battle 11a infurnace 11.

With any change of such pressure drops, manometer 164 through movablecontact 164a will energize motor 160 for rotation in one direction orthe other to change the relative positions of dampers 13 and 17 toequalize said differentials of pressure. Such an operation iscontemplated, but in order to provide greater flexibility and to make iteasy to maintain any desired division of flow of combustion air and anydesired rate of combustion in the two furnaces, a pressure regulatingvalve 167 and a pneumatic booster or relay 168 are provided betweenlines 141 and 166. Pressure from line 141 is applied by way of a line169 to the lower side of a diaphragm 168a of large diameter as comparedwith a second diaphragm 1681;. A valve element 1680 is normally biasedto open position for flow of air from a source including a regulator 170to a line 171 and thence through valve 167 to line 166. The pressure inline 171 is applied to the upper side of diaphragm 16Sb connected to thevalve stem, and thus opposes the pressure applied to the lower side ofthe larger diaphragm 163a. Accordingly, the position of the valve willdepend upon the balance between these two pressures, neglecting a lightspring which may be included to bias the valve element 1680 to the openposition. Since the diaphragm 168a is of larger diameter, a higherpressure must exist in line 171 for application to the smaller diaphragm1623b in order to balance the forces on the valve stem. Thus thepressure in line 171 will be proportional to that in line 169, buthigher in the ratio of the relative areas of the two diaphragms. Theratio of pressures may be of the order of 1.6. The valve 167 ispreferably of the throttling type with a leak-port so that upon movementas by knob 172 of its stem in one direction, the pressure in line 166may be reduced to any desired degree, to a value lower than or equallingthe pressure in line 171. When in a position to produce equalityasbetween pressures in lines 141 and 166, the

operation will be as described above where the assump tion was made of adirect connection from line 166 to line 141.

When the pressure in line 166 is higher than in line 141, the tiltingmanometer 164 will energize motor 160 for rotation of element 161 in adirection to open damper 17. This will increase the flow of air throughfurnace 15 relative to the flow of air through furnace 11. There willthen be an increased pressure drop across bafile 15a which will resultin an increased pressure in line 165 which is the diagrammatic system ofFig. 3.

applied to the: tilting manometer 164., the change. being in a directionto restore balance. If it be insufficient to restore balance, the motorlo'o'will continue to: rotate in the same direction until dampers 17have. beenmoved to the fully opened position and dampers 1'3 movedtoward the closed position. The change in the differential of pressureacross bafile 11a in furnace 11 and in a decreasing direction will, ofcourse, result in reduced pressure in line 141, as appliedby line 169upon diaphragm 168a to reduce the pressure in line 166, a change whichis also in the direction to restore balance of the manometer 164 and todeenergize motor 160.

Any changes in total flow of combustion air through furnaces 11 and 15.produced by relative adjustments of dampers 13 and 17 is detected bytilting manometer 121; and motor 85 is energized in the direction tomaintain the total flow of air to both furnaces at a predetermined valuerelative to the steam flow in head er 29.

The control of combustion air in the manner which has now been explainedhas been demonstrated to be effectively related to the steam flow fromthe associated vapor generator or steam boiler. The manner in which therate of fuel delivery has been made dependent upon the pressure withinsteam header 29 and upon the oxygen content of the products ofcombustion in the two furnaces has been explained in connection withFig. 1. The requirements of maintaining steam generation to meetvariable loading of the turbine-generator 30 to maintain optimumconditions of combustion are met by the functioning of the two systemswhich, for convenience, sepa-' rately appear in Figs. 1 and 2.

The operation. of dampers 8d, 87 and 88, though described in connectionwith Fig. 1, was not mentioned in the description of the system of Fig.2. The manner in which they are operated to maintain a predeterminedpressure within furnaces 11 and will now be described in The airpressure within each of furnaces 11 and 15 is applied, respectively, byway of lines 175 and 176 to manometers 177 and 178. Since in most casesit will be desired to maintain the pressures within the furnaces in theneighborhood of atmospheric pressure, the manometer 177 may be providedwith a counterbalance weight 177a on the tilting arm thereof on one sideof the fulcrum, while on the opposite side thereof the pressure fromfurnace 11 is applied by way of lines 175 and 179 to a liquid-sealedchamber 180., while the pressure from furnace 15 is applied by way oflines 176 and 181 to a liquid-sealed chamber 182. Thus, the tilting armof manometer 177 has a torque applied to it tending to rotate it in acounterclockwise direction with pressures in chambers 180 and 182 belowatmospheric and in a clockwise direction with pressures aboveatmospheric.

As shown, the pressures within the furnaces 11 and 15 are slightly belowatmospheric and the manometer arm is shown exactly balanced by thecounterweight 177a. With a rise in pressure within either or both offurnaces 11 and 15, the manometer 1'77 closes a circuit for motor 89 foroperation of dampers 38 toward closed position to reduce the furnacepressures to values such that their sum as represented by torques on thearm of manometer 177 is equal to the torque applied to it by thecounterweight 177a. In order that not only the sum of the pressuresshall be maintained at a predetermined value, but also so that thepressures within the two furnaces may be at all times equalized, lines175 and 176 are connected to a differential tilting manometer 178 whichresponds to any difference between them to energize a motor 183 in adirection to move dampers 86 toward closed position with dampers 87 intheir fully opened position or, as shown, to move dampers 87 towardclosed position with dampers 86 in the fully open position.Schematically, an actuating element 184 and associated push rodsfunction in the same manner as described for the actuatins elemen lfil.f? g. 2 and. he e, ne d no asainb described in detail. I

Mention has already been made of the fact that variables other thanoxygen content of the products of combustion may be utilized to maintainoptimum conditions of combustion within the furnaces 11 and .15, suchfor example, as carbon dioxide. However, the oxygen-content detectingsystem has been illustrated in Fig. 4 where there is .shown in detailthe apparatus included in each of the blocks 31 and 32 of Fig. 1. InFig. 4 sampling elements 31a and 32aare illustrated as pipe linesthrough which products of combustion are withdrawn. from the respectivefurnaces 11 and 15 as by applying suction to the flow lines. In each oflines 31a and, 32a there are provided filters and 191 to preventtransfer of solid products into flow lines 1 92 and 193.

The apparatus illustrated within the blocks 31 and 32 is fully describedin Foley et a1 Patent. No. 2,603,964 and, hence, need not here bedescribed in detail. For convenience, the applicable referencecharacters used in the Foley et al. patent, Fig. 9, have been applied tothe present Fig. 4, but in the 200 series.

Filtered products of combustion flowing through line 192 are passedthrough gas cells 215 and 214 and exit from the .outlet of an aspirator195 having a fluid inlet pipe 196 for producing reduced pressure onlines 192 and 31a. The cells 214 and 215 are provided with resistorelements 216 and 217. Associated with the cell 214 is a. magnet 223which exerts a strong magnetic field extend-- ing in a directiontransversely of the longitudinal axis and which is preferably shaped toprovide a steep magnetic gradient in a direction perpendicular to thelongitudinal axis of element 216.. Resistor elements 216 and 217 areheated by flow of current therethrough to set up convection currentswithin each cell. In cell 214 the cooling effect of the convectioncurrents is increased due to the accelerating effect of the magneticfield from. the permanent magnet 223.

The mass susceptibility of a paramagnetic gas, such as oxygen, variesinversely as its temperature. Therefore, the cooler paramagnetic gasesadjacent the walls of the cell 214 are directed downwardly toward thezone of maximum magnetic force and into the vicinity of the heatedresistor 216. The magnetic component of flow thusproduced is a functionof the concentration of oxygen in the products of combustion, and sincethis flow component is in a direction to augment the cooling effect onresistor 216, its temperature will be lowered below that ofcorresponding resistor 217 in cell 215. The resistances will differ byan amount directly related to the concentration of the oxygen content ofthe gas.

The above brief explanation applies, of course, to the other cells shownin Fig. 4. To measure the oxygen content, the resistor elements 216 and217 are connected in two arms of a Wheatstone bridge 250, additionalresistor elements 227 and 228 forming the other two arms of the bridge.The bridge is energized from alternatingcurrent supply lines, and theunbalanced output is applied to an amplifier 230 in opposition to theoutput of a bridge 254 provided with elements functioning in mannersimilar to those described in the bridge 250 but exposed to aparamagnetic gas of known concentration of oxygen, such for example, asthe oxygen-containing atmosphere. The flow path includes filter 190a,cells 215a and 214a and the aspirator 195a.

The output from bridge 250 is derived across the resistor 263a and theoutput from bridge 254 is derived across a slidewire resistor 263. Themovable contact 263b is adjustable by motor 197 in response to adifference between the output of bridge 250 and that of a bridge 254 ina direction to bring the fractional part of the output voltage of bridge254 to a value equal to the output of bridge 250. Thus, the ratio of theunbalances of the two bridge circuits 250 and 254 provides a relativemeasure of the oxygen content of the gases from furuacell. The motor 197may be used to operate a pen-index 198 of a recorder 199 and alsorelatively to adjust contact 34a relative to its slidewire 34.

' The apparatus in block 32 functions for the furnace in exactly themanner described for furnace 11, and the parts of the two bridges 350and 354 have been given like reference characters with those of saidpatent, except they are in the 300 series.

The oxygen content of the gases from furnace 15 is measured and recordedby a recorder 199a driven by a motor 197a and that motor also relativelyadjusts contact 33:: relative to its slidewire 33. The Wheatstone bridge35 energized from an alternating-current source of supply has an outputproportional to the difference between the oxygen content of the gasesin furnace 11 and those in furnace 15. The operation of the bridge 35has already been described in connection with Fig. 1 and will not herebe repeated.

The control system shown by block 36 within bridge.

35 of Fig. 1 may comprise the amplifier shown in Fig. 1 of Davis PatentNo. 2,530,326. In Fig. 4 of the present case, the output of bridge 35 isapplied to an amplifier 36a corresponding with the amplifier 28 of saidDavis patent, the output thereof serving to energize the operat ing coilof a relay 36b of the single-pole, double-throw type for operation inone direction upon unbalance of the bridge in one direction and foroperation in the opposite direction upon reverse of said unbalance.While the relay may be of the polarized type, it may be also of the typediagrammatically illustrated in said Davis patent, i. e., one responsiveto change in lever of energization, which level occurs upon change ofdirection of unbalance of the bridge. Where carbon dioxide is to be usedas the component of the combustion gases to maintain optimum conditionsof combustion, it will, of course, be understood that a different typeof detecting system should be used, one, such for example, as disclosedin Peters Patent No. 1,504,707.

It is to be further understood that only one of the systems withinrectangles 31 and 32 need be used, suitable provisions being made forsimultaneous transfer, first for the measurement of the oxygen contentWithin furnace 11 and then for the measurement of the oxygen contentwithin furnace 15, the transfer mechanism in each case serving first toadjust contact 3411 and then to adjust the contact 33a in the bridge 35.The advantages of eliminating any need for identical response as betweenand that certain features may be used with other features omitted, andthat other types of control systems may be utilized in conjunction withthe system of maintaining the magnitude of a selected product ofcombustion at a predetermined value. For example, in the modification ofthe invention illustrated in Fig. 5 it will be shown that the flow ofthe combustion air to the respective furnaces need not depend upon steamflow in the header 29. Combustion air may be controlled in response to adifferent type of steam-responsive means, namely, one responding tochanges in steam pressure. For the most part, Fig.

5 corresponds with the air control system of Fig. 2, and

the same parts have, of course, been given the same referencecharacters. However, there has been added to Fig. 5 the mastercontroller 93 of Fig. 1 which through line 91 is connected to the header29 to produce an air pressure in line 100 which varies inversely withchange of steam pressure in line 29. Because of the proportional andreset bellows 105 and 106, the air pressure in line 100 varies withchange in the vapor load upon the vapor generator. With other thansteady-state conditions, the rate function introduced by rate valve 111modifies the air pressure in line 100 and, of course, at least anothercomponent of control action is introduced by the proportional bellows105. After change in steam pressure, following a change in load andsubsequent return of steam pressure in line 29 to its predeterminedvalue, the pressure in line 100 will be established at a new steadyvalue related to the new load.

The master controller 93 continues to function in connection with theKelvin balances and of Fig. 1 directly to regulate the rate of fueldelivery to the respective furnaces 11 and 15. However, the total flowof air to those two furnaces depends upon the setting of dampers 84 bymotor 85. In Fig. 5 motor is energized under the control of asingle-pole, double-throw switch 124a operable by a tilting manometer360 having applied to the lefthand chamber by way of line 361 thepressure on the high side of the restriction 133 and having applied toits righthand chamber the pressure on the low pressure side of saidrestriction by way of line 362. The tendency of the tilting manometer360 to rotate about its pivot in a clockwise direction is opposed by theair pressure applied to a diaphragm 368 having a value determined by theoutput air pressure in line and the setting of a leak-port valve 364which is of the same construction as similar leak valves and 153 of thissame figure.

It will be recalled that the total air flow through restriction 133 isrelated to the total air flow through furnaces 11 and 15 and is made tovary with any change in that air flow. The tilting manometer 360functions in response to any change in air flow through the furnaces asreflected by a change in air flow through restriction 133 to return thetotal air flow to a predetermined value as by energizetion of motor 85in one direction or the other. Similarly, any change in steam pressurereflected by a change in air pressure in line 100 changes the biasexerted on the tilting manometer 360 by diaphragm 368 and causes thesingle-pole double-throw switch 124a to move in a direction to energizemotor 85 to open dampers 84 to increase the total air flow whenever thesteam pressure falls and to decrease the total air flow whenever thesteam pressure in header 29 rises. The modification of Fig. 5 will, insome cases, be preferred to that shown in Fig. 2, and is a modificationto be considered when oil burners or types of fuel other than powderedcoal are to be utilized.

What is claimed is:

1. In combination, a vapor generator having independent furnaces, eachwith its own fuel burner and its own vapor heating sections, saidsections being connected to a common line for delivery of vapor to aload, means responsive to an operating condition of said vapor generatorrepresentative of its vapor load for establishing a predetermined totalair flow to said furnaces, means responsive to an operating condition ofsaid vapor generator representative of the vapor load for increasing thetotal rate of fuel supply to said furnaces with increase in vapor loadand for decreasing said total rate of fuel supply to said furnaces withdecrease in said vapor load, a

sensitive element for each furnace exposed to combustion productsgenerated therein for developing an output which varies with effieiencyof combustion of fuel within said furnace, and means responsive to theoutputs of said sensitive elements for increasing the rate of fuelsupply to one furnace while decreasing the rate of fuel supply to theother furnace until the outputs of said sensitive elements bear apredetermined relation one to the other.

2. In combination, a vapor generator having independent furnaces, eachwith its own fuel burner and its own 1 vapor heating sections, saidsections being connected to a common line for delivery of vapor to aload, means responsive to an operating condition of said vapor generatorrepresentative of its vapor load for establishing a predetermined totalair flow to said furnaces, means responsive to an operating condition ofsaid vapor generator representative of the vapor load for increasing thetotal rate of fuel supply to said furnaces with increase in vapor loadand for decreasing said total rate of fuel supply to said furnaces withdecrease in said vapor load, a sensitive element for each furnaceexposed to combustion products generated therein for developing anoutput which varies with the oxygen content of said combustion products,and means responsive to the outputs of said sensitive elements forincreasing the rate of fuel supply to one furnace while decreasing therate of fuel supply to the other furnace until the outputs of saidsensitive elements bear that predetermined relation one to the otherindicative of oxygen contents representative of optimum conditions ofcombustion of fuel in said furnaces.

3. In combination, a vapor generator having independent furnaces, eachwith its own fuel burner and its own vapor heating sections, saidsections being connected to a common line for delivery of vapor to aload, means responsive to the rate of flow of vapor in said common linefor establishing a predetermined total air flow to said furnaces, meansresponsive to the vapor pressure of said vapor generator for decreasingthe total rate of fuel supply to said furnaces with increase in vaporpressure and for increasing said total rate of fuel supply to saidfurnaces with decrease in said vapor pressure, a sensitive element foreach furnace exposed to combustion products generated therein fordeveloping an output which varies with efiiciency of combustion of fuelwithin said furnace, and means responsive to the outputs of saidsensitive elements for increasing the rate of fuel supply to one furnacewhile decreasing the rate of fuel supply to the other furnace until theoutputs of said sensitive elements bear a predetermined relation one tothe other.

4. In combination, a vapor generator having independent furnaces, eachwith its own fuel burner and its own vapor heating sections, saidsections being connected to a common line for delivery of vapor to aload, means responsive to the vapor pressure of said vapor generator forestablishing a predetermined total air flow to said furnaces, meansresponsive to the vapor pressure of said vapor generator for decreasingthe total rate of fuel supply to said furnaces with increase in vaporpressure and for increasing said total rate of fuel supply to saidfurnaces with decrease in said vapor pressure, a sensitive element foreach furnace exposed to combustion products generated therein fordeveloping an output which varies with efficiency of combustion of fuelwithin said furnace, and means responsive to the outputs of saidsensitive elements for increasing the rate of fuel supply to one furnacewhile decreasing the rate of fuel supply. to the other furnace until theoutputs of said sensitive elements bear a predetermined relation one tothe other.

5. In combination, a vapor generator having independent furnaces, eachwith its own fuel burner and its own vapor heating sections, saidsections being connected to a common line for delivery of vapor to aload, means responsive to an operating condition of said vapor generatorrepresentative of its vapor load for establishing a predeter mined totalair flow to said furnaces, means responsive to an operating condition ofsaid vapor generator representative of the vapor load for increasing thetotal rate of fuel supply to said furnaces with increase in vapor loadand for decreasing said total rate of fuel supply to said furnaces withdecrease in said vapor load, a sensitive element for each furnaceexposed to combustion products generated therein for developing anelectrical output which varies with efficiency of combustion of fuelwithin said furnace, means including a network for producing an outputrelated to the difference between said electrical outputs from saidelements, and means responsive to said output of said network formodifying the fuel supply to the burners of one of said furnacesrelative to the fuel i4 supply to the other of said furnaces withoutchanging said total rate of fuel supply to said furnaces until saidelectrical outputs of each of said sensitive elements bears apredetermined relation one to the other.

6. in combination, a vapor generator having independent furnaces, eachwith its own fuel burner and its own vapor heating sections, saidsections being connected to a common line for delivery of vapor to aload, means responsive to an operating condition of said Vapor generatorrepresentative of its vapor load for es= tablishing a predeterminedtotal air flow to said fur naces, means responsive to an operatingcondition of said vapor generator representative of the vapor load forincreasing the total rate of fuel supply to said furnaces with increasein vapor load and for decreasing said total rate of fuel supply to saidfurnaces with decrease in said vapor load, a sensitive element for eachfurnace exposed to combustion products generated therein for developingan electrical output which varies with the oxygen content of saidcombustion products, means including a network for producing an outputrelated to the difference between said electrical outputs from saidelements, and means responsive to said output of said network formodifying the fuel supply to the burners of one of said furnacesrelative to the fuel supply to the other of said furnaces withoutchanging said total rate of fuel supply to said furnaces until saidelectrical outputs of each of said sensitive elements bears apredetermined relation one to the other.

7. In combination, a vapor generator having independent furnaces eachwith its own fuel burner, its own vapor heating sections and its ownmeans for regulating the flow of combustion air thereto, said vaporheating sections being connected to a common line for delivery of vaporto a load, means responsive to vapor flow in said line for regulatingthe total amount of combustion air flowing into said furnaces and inamount related to the vapor flow in said common line, means responsiveto the pressure of vapor within said line for decreasing the total rateof fuel supply to the burners of said furnaces with increase of pressurewithin said line and for increasing said fuel supply with decrease ofpressure within said line, a sensitive element for each furnace exposedto combustion products generated therein for developing an output whichvaries with oxygen content of the combustion gases within its saidfurnace, means for comparing the outputs of said sensitive elements, andmeans for relatively varying the fuel supply by said burners to each ofsaid furnaces Without changing said total fuel supply until the outputsof said sensitive elements bear a predetermined relation one to theother for producing like conditions of combustion of fuel within each ofsaid furnaces as reflected by equal oxygen content of the gases therein.

8. In combination, a fluid heater having independent furnaces each withits own fuel burners, its own heating sections and its own means forregulating the flow of combustion air thereto, said fluid heatingsections being connected to a common line for flow of fluid to a load,means responsive to the fiuid load upon said heater for producing aforce varying with change in said load, means responsive to the sum ofthe flows of combustion air through said furnaces for developing anopposing force varying in magnitude with change in the sum of said flowsof combustion air, means for increasing the flow of combustion air withincrease in flow of fluid in said line and for decreasing the flow ofcombustion air with decrease of flow of fluid in said line, meansresponsive to decrease in pressure within said line for simultaneouslyincreasing the rate of fuel supply to said burners of said furnaces andfor decreasing said fuel supply upon increase of pressure in said line,a sensitive element for each furnace exposed to combustion productsgenerated therein for developing an output which varies with efficiencyof combustion of fuel within its said furnace, means including a networkfor producing an output related to the difierence between the outputsfrom said elements, and means responsive to the output of said networkfor modifying the fuel supply to the burners of one of said furnacesrelative to the fuel supplied to the other of said furnaces until theoutputs of each of said sensitive elements bears a predeterminedrelation one to the other.

9. The combustion set forth in claim 8 in which said sensitive elementscomprise paramagnetic detectors for producing outputs representative ofthe magnitude of the paramagnetic gases contained in said combustionproducts.

10. The combination set forth in claim 8 in which said means forcontrolling the rate of supply of fuel to 15 2,328,499

for varying the energization of said Kelvin balances in response tochange in the relative outputs of said sensitive devices.

References Cited in the file of this patent UNITED STATES PATENTS382,489 Pratt May 8, 1888 935,763 Mailloux Oct. 5, 1909 1,166,758 GibsonJan. 4, 1916 1,931,948 Armacost Oct. 24, 1933 2,052,375 Wunsch Aug. 25,1936 2,259,417 Gorrie Oct. 14, 1941 '1943 Saathofi Aug. 31,

